Freshwater mussel Echyridella spp.

Description

• Oval-shapped shell, hinged in centre.
• Shell is dark coloured with gold tinges.
• Occasionally an orange or other coloured encrustation on the shell may be present, as a result of a build up of minerals from surrounding waters.

Taxonomy

There are currently three freshwater mussels in the genus Echyridella which are listed as Threatened or At Risk:

• Echyridella aucklandica, found in the North Island and in the South Island from Lake Manapouri to Lake Hauroko, and classified as Threatened: Nationally Vulnerable;
• Echyridella menziesii, found throughout New Zealand, and classified as At Risk: Declining; and
• Echyridella onekaka, found in north west Nelson, and classified as At Risk: Naturally Uncommon.

Interesting Facts

• Kākahi are unique to New Zealand.
• Widespread throughout New Zealand, in habitats ranging from small, fast-flowing streams to rivers and lakes.
• Are a valuable mahinga kai species.
• Have a complex lifecyle - their parasitic larvae attach to a host fish (most commonly koaro) and once carried upstream they drop off into soft, sandy sediments of rivers and lakes.
• Are long-lived, up to 50 years or more.
• Filter feed, in the same way that other shellfish do.

Association with Plantations

• Can occur in plantation forestry areas.
• Plantation streams and lakes often have relatively high populations of indigenous species.

Threats

• Destruction of riparian vegetation.
• Disturbance of banks and beds of waterways.
• Harvesting.
• Habitat destruction from:
  • Modification of riparian margins.
  • Introduction of aquatic weeds.
  • Siltation.
  • Eutrophication (high nutrients).
  • Erosion of banks through grazing by livestock, goats and deer.
  • Artificial barriers to upstream migration (e.g. culverts, fords with large lips creating a drop off).
  • Depleted flows caused by water abstraction.

Management Options and Methods

• Maintain corridors of riparian vegetation along banks. Corridors should be as extensive as possible (refer to Buxton 1991).
• If possible, expand width of riparian zones during later rotation planting.
• Exclude livestock from riparian areas.
• Control deer and goats that could enter riparian areas.
• Comply with best forest operational management practices to avoid damage to riparian areas.
• Manage or prevent water abstraction from critical habitat areas.
• Regulate or prevent harvesting of threatened species.
• Prevent introductions of exotic fish.
• Prevent introductions of aquatic weeds. Educate local users of weed threats and how to prevent spread.

Monitoring Options

• Undertake surveys to identify presences of species and habitats.
• Consider repeating surveys every few years to ascertain whether key species are still present.
• Liaise with DOC about survey and monitoring methods.
• Report findings to DOC.
• Periodic checks of banks to ensure compliance with best forest operational management practices, pest and weed levels and siltation.

Further Information and Support

• DOC – advice for management, survey, and monitoring. Website http://www.doc.govt.nz/
• James, M. 1987. Ecology of the freshwater mussel, Hyridella menziesi (Gray) in a small oligotrophic lake. Arch. Hydrobiol. 108: 337-348.
• NIWA website. http://www.niwa.cri.nz